1. Field of The Invention
This invention relates to novel silacyclohexane compounds and the preparation thereof. The invention also relates to intermediate compounds for the silacyclohexane compounds, to liquid crystal compositions comprising the silacyclohexane compound or compounds, and to devices comprising the compositions.
2. Description of the Prior Art
The liquid crystal display devices utilize optical anisotropy and dielectric anisotropy of liquid crystal substances. Depending on the mode of display, different types of display systems are known including those of a twisted nematic type (TN type), a supertwisted nematic type (STN type), a super birefringence type (SBE type), a dynamic scattering type (DS type), a guest/host type, a type of deformation of aligned phase (DAP type), a polymer dispersion type (PD type), and an optical mode interference type (OMI type). The most popular display device is one which is based on the Schadt-Helfrich effect and has a twisted nematic structure.
Although the properties of the liquid crystal substances used in these liquid crystal devices depend, more or less, on the type of display, it is commonly required that the liquid crystal substances have a wide range of temperatures working as a liquid crystal and that they be stable against moisture, air, light, heat, electric field and the like. Moreover, the liquid crystal substances should desirably be low in viscosity and should ensure a short address time, a low threshold voltage and a high contrast in cells.
Liquid substances which can satisfy all the requirements have never been known when used singly. In practice, several to ten and several liquid compounds and/or latent liquid crystal compounds are used in the form of a mixture. To this end, it is important that constituent components be readily compatible with one another.
Existing liquid crystal compounds usable as these constituent components include those compounds which have a cyclohexyl ring-butylene-phenyl ring (QPCH) structure or a cyclohexyl ring-cyclohexyl ring-butylene-phenyl ring (QPCC) structure.
As liquid crystal display devices have wider utility in various fields, the characteristic properties required for liquid crystal materials become severer. In fact, liquid crystal materials now demanded should have an improved low temperature performance, a wider working temperature satisfying on-vehicle needs and a lower drive voltage on comparison with existing liquid crystal materials or compositions.